Currently, there are few, if any, inexpensive cooling systems that do not require continuously available energy input. For example, compression refrigeration systems require continuous electrical energy input, and ammonia absorption refrigeration systems require continuous heat input. Other systems that use alternative energy sources are immense in scale and unsuitable on a smaller scale and typically require suitable energy (e.g., electrical energy) for running pumps and other instrumentation.
Electrical energy is convenient but is becoming expensive and can have a large CO2 footprint or problems associated with nuclear waste. Blackouts can also be a common occurrence worldwide, particularly in developing economies. Furthermore, it is desirable to reduce or eliminate ozone layer depleting emissions from conventional chlorofluorocarbon (CFC)-based vapor compression cooling equipment. Even in areas where electrical energy is readily available, it is desirable to increase the use of renewable energy such as solar energy.
Thus, it is desirable to have cooling devices working even when no electrical or conventional energy is available. For example, it is desirable to have a room cooling device working in cities of India even when there is no electrical supply available as happens so frequently due to load shedding or rolling blackouts. It is also desirable to decrease the use of conventional energy. The same is true in places like Arizona even though continuous supply of electricity may be available.
More than 30% of the energy consumed in the world is used for heating and/or cooling of buildings. Research on cooling systems generally focuses on one of two parts: (1) minimizing heat gains, or (2) optimizing cooling technologies, which can increase efficiency and lower energy costs without decreasing performance. Solar cooling can be an attractive alternative to fossil fuel powered cooling because the demand for cooling is usually greatest when there is an abundance of solar energy available.